Portable radial stackers have been used for many years to stack bulk materials such as aggregate for road construction, grain, coal, and mulch. Radial stackers, which swing around in a radius to stack material in an arc, permit substantially more material to be stacked than is possible using a conventional stationary stacker that permits only a conical stack. Telescoping radial stackers permit even more material to be stacked as the stacker is extended or retracted during conveying operations.
Radial stackers typically include a wheeled axle disposed between a hopper and the top of the stacker from which the material is discharged. These wheels permit the stacker to be swung in an arc, with the hopper including a pivot plate on which the stacker pivots.
An additional advantage of having a wheeled radial stacker is that the stacker may be folded over itself and be ready for road transport in relatively little time, as the wheels that are used for radial travel can be displaced into a position aligned with the stacker to support the stacker for travel.
In recent years, tracked drives have been used in quarries, agricultural and mining operations to enable equipment to be moved over harsh terrain for ideal positioning for stacking operations. While tracked vehicles have proven to be of great benefit for such purposes, the use of tracks instead of wheels makes it more difficult to shift a stacker radially to facilitate the stacking of material in an arc instead of a cone. Also, because tracked vehicles are not typically permitted to be driven on road surfaces, they are normally loaded onto flatbed trucks for transit from one work site to another. These two drawbacks with the use of tracks has to a certain extent limited the use of tracked vehicles.
While portable radial stackers are extremely versatile in that they can operated on a wide variety of terrain and in a variety of conditions, certain materials to be stacked create unique problems. Given the requirement that stacking conveyors need to be able to stack in large, high piles, it is necessary that the angle of inclination of the conveyor be relatively steep, often as steep as 25 degrees or more. This is also true when the conveyors are being used to load ships that might be riding high in the water.
While the inclination issue may not be a problem with some bulk materials that exhibit a high degree of friction on the conveyor belt, other materials such as river rock and salt do not exhibit such friction. Special conveyor belts bearing ribs or other friction-increasing features may be used to convey such low-friction materials but this may require removal and replacement of the belt, which is not an easy task to complete on site. It is also necessary that conveyors be able to operate in a wide variety of weather conditions, such as rain, snow and ice. Bulk materials that can be conveyed at a steep angle when dry might be more difficult to convey in the presence of moisture or winter conditions. While the angle of inclination is adjustable in most portable radial conveyors, reducing the angle of inclination will often substantially reduce the size or height of the piles into which the stacker can deposit bulk material.